# MOO and VRML

"Robert J. Brown" (rj@eli.wariat.org)
Sat, 17 Feb 1996 12:17:48 PST

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    >>>>> "Dmitri" == Dmitri Kondratiev <dima@paragraph.com> writes:

        Dmitri> I don't know any other working architecture of distributed
        Dmitri> VR of today, except for DIS, which is "war-games" oriented
        Dmitri> only. Do you ?

    [from my resume at http://eli.wariat.org/~rj/resume/resume.html]

    LORAL DEFENSE SYSTEMS. 1993-1994. Consultant Helped the client
        implement CTES (Common Tactical Environment Simulator), a reusable
        component for DIS (Distributed Interactive Simulation) combat
        trainer/simulators. CTES is a virtual reality component for networked
        simulators that simulates a world in which humans participate. This
        world is mirrored on each node on the defense simulation internet
        (DSI) that is participating in the simulation. I led the development
        team that was responsible for all the executive and communications
        components of CTES. I personally designed the scheduling and
        dispatching components, and guided the design of the shared memory and
        Ethernet communications component, and the object instantiation
        component, which included dynamic binding to other objects at
        instantiation time.

    This propject was written in C++ with an eye towards ultimate
    conversion to Ada-9X (now Ada-95).  We were really pushing the
    envelope of what DIS was capable of on this project.  We actually had
    our own internal representation for everything and only wrapped it up
    in DIS packets to satisfy contractual requirements.  It would have been
    a lot easier if we could have chosen the representation.

    The overall architecture involved having a bunch of objects that all
    lived on all the machines.  A given machine had the human in control
    of any non-fictive object (an object operated by a person, instead of
    a state machine or production rules), and other non-fictives had
    humans on other (or perhaps the same) machines.  Everything was
    message passing.  Message passing had to operate over shared memory
    and over networks, so no pointers, etc. allowed in messages.

    Every message was time-stamped with its delivery time, not its
    origination time.  Think of it like a "do not open until Christmas"
    warning on the envelope.  This way, if a message could be sent before
    it was needed to be acted upon, then it allowed for a certain amount
    of not-lag and still gave good fidelity.  Dealing with anachronistic
    message arrivals can mean having to undo some action or side-effect :-(

    The really demanding part of this DIS stuff is the speed things happen
    with.  A fighter plane heqading north at Mach speed approaching an
    enemy air-to-air missle at Mach speed fires an interceptor at Mach+
    speed.  These targets are born and die in a few seconds, and there is
    a *LOT* of action, including real-time video, in the meanwhile.

    In a MOO, things generally happen at pedestrian speeds, which is a lot
    easier.  Message deliveries are critical to within a second or so, not
    a few miliseconds or so.  There is less need for animated fictives, as
    we have lots of real people participating.  The only real difficulty
    is in maintaining active state for mirror objects on machines that do
    not host the owning person for that object.

    I think educational/conferencing/social moos in message passing
    peer-to-peer VR are quite doable.  Shoot-em-up MUDs could present a
    problem if the action got too fast with a lot of players in the same
    virtual location.  But then, *I* don't care about shoot-em-up's :-)
    [except professionally, when I get paid to care.]

    --
    -----------  "...  And the men went up and viewed Ai."  [Jos 7:2]  -----------
    Robert Jay Brown III  rj@eli.wariat.org  http://eli.wariat.org  1 847 705-0370
    Elijah Laboratories Inc;  759 Independence Drive;  Suite 5;  Palatine IL 60074
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